A Cancellation (or Postponement) with the cancellation_title filled in will be shown in the list of upcoming or past events at the date the event was cancelled. This matches how cancellations are already displayed in the monthly and weekly calendar views.
- Don't build unnecessary holiday objects
- Fix weekly urls at the end of the year
- Use None to mark default byweekday and bymonth
- Count PermissionDenied errors in import as failures